1. Field of the Invention
The subject invention is directed to exhaust mufflers manufactured substantially from formed components, such as stamp formed sheets of metal.
2. Description of the Prior Art
The typical prior art exhaust muffler includes a plurality of separate parallel tubes that are supported by transversely extending baffles. The baffles typically are of oval or circular shape. The assembly of tubes and baffles is slid into a tubular shell having a shape conforming to the shape of the baffles. An outer wrapper may be wrapped around the shell for additional strength and for noise insulation. Opposed end caps are then mechanically connected to the ends of the shell and wrapper to enclose the muffler. The end caps include apertures to define an inlet and an outlet on the muffler. The most common prior art mufflers include a single inlet in one end cap of the muffler and a single outlet in the opposed end cap. However, other configurations of inlets and outlets are possible and are used periodically to accommodate the particular needs of an exhaust system.
Chambers are formed within the above described prior art muffler between adjacent baffles or between a baffle and an end cap. Selected tubes within the muffler may be perforated or louvered to permit a controlled expansion of exhaust gas into the surrounding chamber. Other tubes may have their end in a particular chamber so that all gas flowing through that tube will empty into the associated chamber. The particular dimensions of the tubes, chambers and apertures or louvers will be selected to efficiently attenuate the noise associated with the exhaust gas flowing from the engine.
The primary flow of exhaust gas in the above described prior art muffler is generally parallel to the axis of the tubular outer shell. However the flowing exhaust gas will periodically reverse directions in chambers formed adjacent the end caps. A secondary flow of exhaust gas may occur as the exhaust gas expands through the perforations or louvers in a tube and into surrounding chambers. Prior art mufflers with tubular outer shells generally have not included chamber walls that extend parallel to the axis of the outer shell.
The prior art mufflers described above generally perform very well. However, these mufflers include a large number of separate parts that must be assembled in a labor intensive manufacturing process. Additionally, these prior art mufflers are limited to substantially tubular shapes with few options for location and alignment of the inlet and outlet of the muffler.
The prior art also includes mufflers made substantially from a plurality of formed sheets of metal. The typical prior art stamp formed muffler includes a pair of internal plates that are formed with channels. The internal plates are secured in face-to-face relationship such that oppositely directed channels substantially register with one another and define tubes for accommodating the flowing exhaust gas. Portions of these stamp formed tubes may be perforated or louvered to permit an expansion of exhaust gas therefrom. The typical prior art stamp formed muffler further includes a pair of outer shells. Each outer shell is stamped to define a generally planar peripheral flange. At least one chamber extends from the plane of the peripheral flange. The peripheral flanges of these outer shells are secured to peripheral regions of the internal plates such that the chambers surround the array of tubes defined by the internal plates.
Typically each tube of the prior art stamp formed muffler will communicate simultaneously with the chambers on opposite sides of the respective internal plates. However, an exception is U.S. Pat. No. 4,765,437 which has first and second internal plates formed to define first and second substantially parallel tuning tubes. A first external shell defines a first low frequency resonating chamber surrounding the first internal plate, while a second external shell defines a second low frequency resonating chamber surrounding the second internal plate. Portions of the first plate that define a first tuning tube include an opening to permit the first tuning tube to communicate with the first low frequency resonating chamber. However, portions of the second tuning tube defined by the first internal plate have no opening. Hence the second tuning tube does not communicate with the first low frequency resonating chamber. Portions of the second internal plate defining the second tuning tube have an opening to permit the second tuning tube to communicate with the second low frequency resonating chamber. However, portions of the second internal plate defining the first tuning tube have no opening. Thus, if the internal plates are aligned horizontally, the first tuning tube may communicate with a top low frequency resonating chamber, while the second tuning tube may communicate with a bottom low frequency resonating chamber. Flow patterns of this type generally were not possible with the prior art conventional muffler with a wrapped outer shell. U.S. Pat. No. 5,004,069 shows a somewhat similar concept applied to expansion chambers.
Exhaust mufflers typically create a back pressure on the flowing exhaust gas. Back pressure retards engine performance, and hence an exhaust muffler should be designed to achieve its noise attenuating function without an unacceptably high back pressure. Stamp formed mufflers generally permit curved surfaces that are not possible with conventional mufflers employing standard tubes and wrapped outer shells. Curved surfaces reduce back pressure and improve engine performance. Back pressure may be further decreased by utilizing the maximum volume available for the flowing exhaust gas. In this regard, a large tube or large chamber is generally less restrictive than a smaller tube or smaller chamber for accommodating a flowing exhaust gas. A stamp formed muffler with effective use of curved surfaces to reduce back pressure is shown, for example, in U.S. Pat. No. 5,252,788. A stamp formed muffler that relies largely upon a plurality of in-line flow chambers in an effort to avoid high back pressure is shown in U.S. Pat. No. 5,173,577. In this latter muffler, each of the in-line flow chambers is disposed between the internal plates of the muffler. Certain of these in-line flow chambers or in-line flow tubes may be perforated to permit expansion of exhaust gas into surrounding chambers defined by the external shells. However, these chambers defined by the external shells are not part of the primary flow path of exhaust gas moving from the inlet to the outlet of the muffler.
The hot flowing exhaust gas typically includes caustic vapors. These vapors will condense when the engine is shut off and the muffler is permitted to cool. The caustic condensate will accumulate at the gravitational low point of the muffler, and may corrode the metal from which the muffler is formed. Various attempts have been made to prevent muffler corrosion. For example, some mufflers simply provide a drainage hole at the gravitational low point. However, the drainage hole can become clogged. Furthermore, some new car manufacturers will not permit drainage holes. Other mufflers provide a siphon tube extending from the gravitational low point to the outlet tube of the muffler. Pressure differentials between the gravitational low point in the chamber and the outlet tube will cause the flowing exhaust gas to effectively suck liquid from the gravitational low point. The incorporation of a separate siphon tube into a conventional muffler requires complex welding and additional costs. A stamp formed muffler with a separate siphon tube is shown in U.S. Pat. No. 5,563,385. A stamp formed muffler with a stamp formed siphon tube is shown in U.S. Pat. No. 5,563,383.
In view of the above, it is an object of the subject invention to provide a muffler manufactured substantially from stamped components with an enhanced ability to attenuate noise while maintaining a desirably low back pressure.
It is a further object of the subject invention to provide a stamp formed muffler with large flow paths and in-line flow chamber for the exhaust gas.
A further object of the subject invention is to provide a muffler having a plurality of in-line flow chambers separated from one another by internal plates of the muffler.
Still a further object of the subject invention is to provide a muffler that can effectively siphon exhaust gas from the gravitational low point of the muffler without providing separate siphon tubes.